3D hierarchical tri-doped porous carbon derived from calcium lignosulfonate for high-performance zinc ion hybrid capacitors

Zinc-ion hybrid capacitors with neutral electrolytes have good safety, excellent power density, and energy density. However, zinc-ion hybrid capacitors rely on expensive porous carbon cathode materials. Additional chemical reagents are required to activate precursor during the pore-forming process. Therefore, it is essential to develop porous carbon with low preparation costs and high performance. In this work, low-cost calcium lignosulfonate (CLS) as a carbon source was used to prepare N, O, and S tri-doped hierarchical porous carbon (LHPC) by a one-step carbonization method without additional pore-forming agents. During high-temperature carbonization, the self-pyrolysis of CLS yields a variety of gaseous products as well as inorganic salts like calcium carbonate and calcium sulfate, which work as pore-forming agents. Used as a cathode, LHPC-700 was assembled into an asymmetric zinc ion electrochemical capacitor. The capacitor exhibits a gravimetric specific capacitance of 178.7 F g-1 at a current density of 0.1 A g-1 and an energy density of 63.5 W h kg-1. This study provides an idea for the sustainable utilization of lignin resources to prepare three-dimensional hierarchical porous carbon electrode materials. Low-cost calcium lignosulfonate (CLS) as a carbon source was used to prepare N, O, and S tri-doped hierarchical porous carbon (LHPC) electrode material by a one-step carbonization method without additional pore-forming agents.